Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $69.72   5.542%   $73.5839   $73.58   $73.60   $73.60  
  Purchase #2 $38.80   4.687%   $40.6186   $40.62   $40.60   $40.60  
  Purchase #3 $90.95   5.291%   $95.7622   $95.76   $95.75   $95.80  
  Purchase #4 $215.28   12.679%   $242.5754   $242.58   $242.60   $242.60  
  Purchase #5 $223.39   9.512%   $244.6389   $244.64   $244.65   $244.60  
  Purchase #6 $51.74   11.367%   $57.6213   $57.62   $57.60   $57.60  
  Purchase #7 $18.80   3.722%   $19.4997   $19.50   $19.50   $19.50  
  7 purchase totals = $708.68       $774.3000   $774.30   $774.30   $774.30